Filing of criminal charges would not be surprising in this case.
The robber was fleeing the scene, not advancing upon the victim.
Robber got shot in the backside, not the frontside. Basically, the Shooter used Lethal Force. [Just didn't happen to be lethal in this case.]
However, it is Very Hard for the Shooter to offer the defense that he feared Great Bodily Harm or Loss of His Own Life when the Perp was actually running away from the scene of the crime.
Yeah--I know. I think it would be a Crock, too.
But what we think is Good Sense and what is The Law thinks are often on separate tracks.
When I was a Kid---admittedly a While Ago---the Cops could call out, "Halt, or I'll Shoot!" Then they could shoot. And did. Sometimes it was said that they got the order mixed up.
We live in different times.